A monoclonal antibody against HLA-A11 and A24

Identification of HLA-A*24:02-Restricted CTL Candidate Epitopes Derived from the Nonstructural Polyprotein 1a of SARS-CoV-2 and Analysis of Their Conservation Using the Mutation Database of SARS-CoV-2 Variants

COVID-19 vaccines are currently being administered worldwide and playing a critical role in controlling the pandemic. They have been designed to elicit neutralizing antibodies against Spike protein of the original SARS-CoV-2, and hence they are less effective against SARS-CoV-2 variants with mutated Spike than the original virus. It is possible that novel variants with abilities of enhanced transmissibility and/or immunoevasion will appear in the near future and perfectly escape from vaccine-elicited immunity. Therefore, the current vaccines may need to be improved to compensate for the viral evolution. For this purpose, it may be beneficial to take advantage of CD8+ cytotoxic T lymphocytes (CTLs). Several lines of evidence suggest the contribution of CTLs on the viral control in COVID-19, and CTLs target a wide range of proteins involving comparatively conserved nonstructural proteins. Here, we identified 22 HLA-A*24:02-restricted CTL candidate epitopes derived from the nonstructural polyprotein 1a (pp1a) of SARS-CoV-2 using computational algorithms, HLA-A*24:02 transgenic mice and the peptide-encapsulated liposomes. We focused on pp1a and HLA-A*24:02 because pp1a is relatively conserved and HLA-A*24:02 is predominant in East Asians such as Japanese. The conservation analysis revealed that the amino acid sequences of 7 out of the 22 epitopes were hardly affected by a number of mutations in the Sequence Read Archive database of SARS-CoV-2 variants. The information of such conserved epitopes might be useful for designing the next-generation COVID-19 vaccine that is universally effective against any SARS-CoV-2 variants by the induction of both anti-Spike neutralizing antibodies and CTLs specific for conserved epitopes. IMPORTANCE COVID-19 vaccines have been designed to elicit neutralizing antibodies against the Spike protein of the original SARS-CoV-2, and hence they are less effective against variants. It is possible that novel variants will appear and escape from vaccine-elicited immunity. Therefore, the current vaccines may need to be improved to compensate for the viral evolution. For this purpose, it may be beneficial to take advantage of CD8+ cytotoxic T lymphocytes (CTLs). Here, we identified 22 HLA-A*24:02-restricted CTL candidate epitopes derived from the nonstructural polyprotein 1a (pp1a) of SARS-CoV-2. We focused on pp1a and HLA-A*24:02 because pp1a is conserved and HLA-A*24:02 is predominant in East Asians. The conservation analysis revealed that the amino acid sequences of 7 out of the 22 epitopes were hardly affected by mutations in the database of SARS-CoV-2 variants. The information might be useful for designing the next-generation COVID-19 vaccine that is universally effective against any variants.

Development of a novel monoclonal antibody that binds to most HLA-A allomorphs in a conformation-dependent yet peptide-promiscuous fashion

Specificity analyses of peptide binding to human leukocyte antigen (HLA)-A molecules have been hampered due to a lack of proper monoclonal antibodies (mAbs) for certain allomorphs, such as the prevalent HLA-A1 for Caucasians and HLA-A11 for Asians. We developed a mAb that recognizes a conformational epitope common to most HLA-A allomorphs. The mAb, named A-1, does not discriminate peptides by amino acid sequences, making it suitable for measuring peptide binding. A stabilization assay using TAP-deficient cell lines and A-1 was developed to investigate the specificity of peptide binding to HLA-A molecules. Regarding the evolution of HLA-A genes, the A-1 epitope has been conserved among most HLA-A allomorphs but was lost when the HLA-A gene diversified into the HLA-A*32, HLA-A*31, and HLA-A*33 lineages together with HLA-A*29 after bifurcating from the HLA-A*25 and HLA-A*26 branchs. The establishment of A-1 is expected to help researchers investigate the peptide repertoire and develop computational tools to identify cognate peptides. Since no HLA-A locus-specific mAb has been available, A-1 will also be useful for analyzing the locus-specific regulation of the HLA gene expression.

Comparison of speedy PCR-ssp method and serological typing of HLA-A24 for Japanese cancer patients

Human leukocyte antigen (HLA) typing is essential to carry out HLA-class I restricted antigenic peptide-based cancer immunotherapy. To establish a one-step polymerase chain reaction-sequence-specific primer (PCR-SSP) method, we designed two novel HLA-A24-specific primer sets and determined the optimal conditions for specific amplification. Then, we performed HLA-A24 typing of two healthy donors' and 17 cancer patients' peripheral blood with serological typing and PCR-SSP typing. Eleven of the 19 cases were determined HLA-A24-positive by the PCR-SSP method precisely; however, five cases showed false positive with serological analysis. Thus, for HLA-A24 typing in the Japanese population, the PCR-SSP method is faster and more accurate than serological typing.

Novel immunodominant peptide presentation strategy: a featured HLA-A*2402-restricted cytotoxic T-lymphocyte epitope stabilized by intrachain hydrogen bonds from severe acute respiratory syndrome coronavirus nucleocapsid protein

Antigenic peptides recognized by virus-specific cytotoxic T lymphocytes (CTLs) are presented by major histocompatibility complex (MHC; or human leukocyte antigen [HLA] in humans) molecules, and the peptide selection and presentation strategy of the host has been studied to guide our understanding of cellular immunity and vaccine development. Here, a severe acute respiratory syndrome coronavirus (SARS-CoV) nucleocapsid (N) protein-derived CTL epitope, N1 (QFKDNVILL), restricted by HLA-A*2402 was identified by a series of in vitro studies, including a computer-assisted algorithm for prediction, stabilization of the peptide by co-refolding with HLA-A*2402 heavy chain and β(2)-microglobulin (β(2)m), and T2-A24 cell binding. Consequently, the antigenicity of the peptide was confirmed by enzyme-linked immunospot (ELISPOT), proliferation assays, and HLA-peptide complex tetramer staining using peripheral blood mononuclear cells (PBMCs) from donors who had recovered from SARS donors. Furthermore, the crystal structure of HLA-A*2402 complexed with peptide N1 was determined, and the featured peptide was characterized with two unexpected intrachain hydrogen bonds which augment the central residues to bulge out of the binding groove. This may contribute to the T-cell receptor (TCR) interaction, showing a host immunodominant peptide presentation strategy. Meanwhile, a rapid and efficient strategy is presented for the determination of naturally presented CTL epitopes in the context of given HLA alleles of interest from long immunogenic overlapping peptides.

Amyloid precursor-like protein 2 association with HLA class I molecules

Amyloid precursor-like protein 2 (APLP2) is a ubiquitously expressed protein. The previously demonstrated functions for APLP2 include binding to the mouse major histocompatibility complex (MHC) class I molecule H-2K(d) and down regulating its cell surface expression. In this study, we have investigated the interaction of APLP2 with the human leukocyte antigen (HLA) class I molecule in human tumor cell lines. APLP2 was readily detected in pancreatic, breast, and prostate tumor lines, although it was found only in very low amounts in lymphoma cell lines. In a pancreatic tumor cell line, HLA class I was extensively co-localized with APLP2 in vesicular compartments following endocytosis of HLA class I molecules. In pancreatic, breast, and prostate tumor lines, APLP2 was bound to the HLA class I molecule. APLP2 was found to bind to HLA-A24, and more strongly to HLA-A2. Increased expression of APLP2 resulted in reduced surface expression of HLA-A2 and HLA-A24. Overall, these studies demonstrate that APLP2 binds to the HLA class I molecule, co-localizes with it in intracellular vesicles, and reduces the level of HLA class I molecule cell surface expression.

Influence of dominant HIV-1 epitopes on HLA-A3/peptide complex formation

The binding of peptides to MHC class I molecules induces MHC/peptide complexes that have specific conformational features. Little is known about the molecular and structural bases required for an optimal MHC/peptide association able to induce a dominant T cell response. We sought to characterize the interaction between purified HLA-A3 molecules and four well known CD8 epitopes from HIV-1 proteins. To define the characteristics of HLA-peptide complex formation and to identify potential structural changes, we used biochemical assays that detect well formed complexes. We tested the amplitude, stability, and kinetic parameters of the interaction between HLA-A3, peptides, and anti-HLA mAbs. Our results show that the four epitopes Nef73-82, Pol325-333, Env37-46, and Gag20-28 bind strongly to HLA-A3 molecules and form very stable complexes that are detected with differential patterns of mAb reactivity. The most striking result is the nonrecognition of the HLA-A3/Gag20-28 complex by the A11.1M mAb specific to HLA-A3/-A11 alleles. To explain this observation, from the data published on HLA-A11 crystallographic structure, we propose molecular models of the HLA-A3 molecule complexed with Nef73-82, Pol325-333, and Gag20-28 epitopes. In the HLA-A3/Gag20-28 complex, we suggest that Arg at position P1 of the peptide may push the alpha2 helix residue Trp-167 of HLA-A3 and affect mAb recognition. Such observations may have great implications for T cell antigen receptor recognition and the immunogenicity of HLA/peptide complexes.

Peptide-loaded dendritic-cell vaccination followed by treatment interruption for chronic HIV-1 infection: a phase 1 trial

Immune response enhanced by therapeutic HIV-1 vaccine may control viral proliferation after discontinuation of highly active antiretroviral therapy (HAART). Although which strategies for therapeutic vaccination are feasible remains controversial, application of dendritic cells (DCs) as a vaccine adjuvant represents a promising approach to improving deteriorated immune function in HIV-1-infected individuals. The safety and efficacy of DC-based vaccine loaded with HIV-1-derived cytotoxic T lymphocytes (CTL) peptides were thus investigated in this study. Autologous DCs loaded with seven CTL peptides with HLA-A*2402 restriction were immunized to four HIV-1-infected individuals under HAART. In terms of safety, peptide-loaded DCs were well tolerated, and only mild local and general symptoms were observed during vaccine administration. ELISPOT assays to detect IFN-gamma production in CD8(+) lymphocytes revealed a limited breadth of responses to immunized peptides in two of four participants, but no response in the remaining two participants. Differences in immunological response might be attributable to the fact that responders displayed higher nadir CD4 counts before starting HAART and were immunized with a larger number of DCs per reactive peptide than non-responders. Discontinuation of HAART after vaccination failed to lower viral set points compared to those before starting HAART. This early outcome warrants further exploration to elucidate the therapeutic value of vaccination with DCs in HIV-1 infection.

Frequent transmission of cytotoxic-T-lymphocyte escape mutants of human immunodeficiency virus type 1 in the highly HLA-A24-positive Japanese population

Although Japan is classified as a country with a low prevalence of human immunodeficiency virus type 1 (HIV-1), domestic sexual transmission has been increasing steadily. Because 70% of the Japanese population expresses HLA-A24 (genotype HLA-A*2402), we wished to assess the effect of the dominant HLA type on the evolution and transmission of HIV-1 among the Japanese population. Twenty-three out of 25 A24-positive Japanese patients had a Y-to-F substitution at the second position [Nef138-10(2F)] in an immunodominant A24-restricted CTL epitope in their HIV-1 nef gene (Nef138-10). None of 12 A24-negative Japanese hemophiliacs but 9 out of 16 patients infected through unprotected sexual intercourse had Nef138-10(2F) (P < 0.01). Two of two A24-positive but none of six A24-negative Australians had Nef138-10(2F). Nef138-10(2F) peptides bound well to the HLA-A*2402 heavy chain; however, Nef138-10(2F) was expressed poorly on the cell surface from the native protein. Thus, HIV-1 with Nef138-10(2F) appears to be a cytotoxic-T-lymphocyte escape mutant and has been transmitted frequently by sexual contact among the highly A24-positive Japanese population.

Downregulation of the proteasome subunits, transporter, and antigen presentation in hepatocellular carcinoma, and their restoration by interferon-gamma

BACKGROUND

In our previous study, expressions of human histocompatibility leukocyte antigens class I molecules (HLA-I) and the transporter associated with antigen processing (TAP) 1/2 genes were investigated in seven hepatocellular carcinoma (HCC) cell lines. Two cell lines, Hep-3B and HuH-7, showed a reduced level of TAP, which might cause the low surface expression of HLA-I. In order to understand the downregulation mechanism of antigen presentation in tumors, the two cell lines were further investigated.

METHODS

Expressions of HLA-I and antigen presentation-related genes were analyzed by flow cytometry and polymerase chain reaction, respectively. Antigen presentation was tested in 51Cr-release assays.

RESULTS

Flow cytometric analyses revealed low surface expression of HLA-I on Hep-3B and HuH-7 cells. Introduction of HLA-A2 gene did not result in a high surface expression of HLA-A2. This suggested the downregulation of HLA-I expression might be related to defects in the antigen presentation machinery. We then examined expression levels of various antigen presentation-related genes. Hep-3B and HuH-7 demonstrated low expression of the low-molecular-weight protein (LMP) 2, LMP7, TAP1, and HLA-I heavy-chain transcripts. The downregulation of these genes was dissolved by treatment with gamma-interferon. Furthermore, allo-specific cytotoxic T lymphocyte (CTL) lines failed to recognize Hep-3B and HuH-7 cells, while they killed IFN-gamma-treated Hep-3B and HuH-7 cells.

CONCLUSIONS

Our results suggest that defects in the antigen presentation-related molecules might cause downregulation of HLA-I expression, antigen presentation, and subsequently, escape from specific CTL killing. The downregulation could be restored by IFN-gamma treatment, suggesting the potential use of IFN-gamma for therapeutic purposes.

MYC overexpression imposes a nonimmunogenic phenotype on Epstein-Barr virus-infected B cells

Lymphoblastoid cell lines, generated by immortalization of normal B cells by Epstein-Barr virus (EBV) in vitro, have strong antigen-presenting capacity, are sensitive to EBV-specific cytotoxic T cells, and are highly allostimulatory in mixed lymphocyte culture. By contrast, EBV-positive Burkitt lymphoma (BL) cells are poor antigen presenters, are not recognized by EBV-specific cytotoxic T cells, and are poorly allostimulatory, which raises the question of whether immunological pressure exerted during BL pathogenesis in vivo has selected for a 'nonimmunogenic' tumor phenotype. The present work addresses this question by examining the immunogenicity/antigenicity of cell lines, generated by conversion of a conditionally immortalized lymphoblastoid cell line to permanent growth independent of EBV-latent proteins by introduction of a constitutively active or tetracycline-regulated c-myc gene (A1 and P493-6 cells, respectively). Compared with its parental lymphoblastoid cell line, A1 cells showed many of the features of the nonimmunogenic BL phenotype, namely poor allostimulatory activity, poor antigen-presenting function associated with impaired proteasomal activity, down-regulation of peptide transporter, reduced HLA class I expression, and an inability to present endogenously expressed EBV-latent proteins to cytotoxic T cells. P493-6 cells, when grown in the presence of estrogen with the exogenous c-myc gene switched off, were strongly immunogenic. The cells had lost their immunogenic potential, however, when grown on a c-myc-driven proliferation program in the absence of estrogen. Deregulation of c-myc, a step central to the development of uncontrolled BL cell growth in vivo, can thus impose a nonimmunogenic phenotype on proliferating human B cells in the absence of any immune pressure.

Introduction of tapasin gene restores surface expression of HLA class I molecules, but not antigen presentation of an HIV envelope peptide in a hepatoma cell line

A hepatoma cell line, Hep G2, reveals the diminished HLA class I surface expression and the reduced expression of LMP2, LMP7, and tapasin transcripts, suggesting that the reduced expression of these transcripts may be associated with the low expression of HLA class I molecules. Introduction of tapasin gene dramatically up-regulates the surface expression of HLA class I molecules on Hep G2 cells, and unexpectedly, enhances the expression of LMP2 and LMP7 transcripts as well. Unlike Hep G2, these tapasin-transfected Hep G2 cells are recognized by allo-specific CTL. However, the transfectant is unable to endogenously present an HIV envelope peptide to an HIV-specific CTL clone, suggesting that a proteasome-independent antigen processing pathway exists and still remains defective in the transfectant. These data may provide significant evidence that the nonproteasomal antigen processing pathway as well as the proteasomal pathway may be impaired in tumor cells to escape immune surveillance performed by CTL.

An HLA-directed molecular and bioinformatics approach identifies new HLA-A11 HIV-1 subtype E cytotoxic T lymphocyte epitopes in HIV-1-infected Thais

Only limited cytotoxic T lymphocyte (CTL) epitope mapping has been done in nonsubtype B HIV-infected persons. We used molecular immunogenetic tools to determine HIV-specific CTL responses in HIV-1 Env subtype E-infected female sex workers (FSWs) from northern Thailand, where more than 50% of the population is HLA-A11 positive. EpiMatrix, a computer-based T cell epitope prediction algorithm, and a manual editing approach were used to predict 77 possible HLA-A11 CTL epitopes in HIV-1, some of which were conserved between subtypes B and E. MHC binding of these peptides was determined in an HLA-A11 stabilization assay, and binding peptides were tested for CTL recognition in eight HLA-A11-positive FSWs. Subtype E versions of known HLA-A2 subtype B HIV epitopes were also tested in four HLA-A2 positive FSWs. CTL responses were detected in all HLA-A11-positive and in three of four HLA-A2-positive persons. Among the 12 FSWs responses to peptides were found to Pol in 9 (75%), Env in 7 (58%), Nef in 5 (42%), and Gag in 5 (42%), and to conserved epitopes in 8 (67%). To identify HLA-A11 CTL epitopes in the absence of prediction tools, it would have been necessary to test almost 3000 10-mer peptides. EpiMatrix and manual predictions reduced this number to 77, of which 26 were MHC binding and 12 were CTL epitopes. Six of these HLA-A11 CTL epitopes have not been previously reported and are located in RT, gp120, and gp41. This report of CTL responses in subtype E-infected individuals defines epitopes that may be useful in HIV pathogenesis or vaccine studies.

Human leukocyte antigen class I gene mutations in cervical cancer

BACKGROUND

Various mechanisms contribute to the loss of human leukocyte antigen (HLA) class I expression that is frequently observed in cancers. Although some single allele losses have been ascribed to mutations in HLA class I genes, direct evidence for this phenomenon in vivo is still lacking. Thus, we investigated whether HLA class I gene mutations could account for the loss of allele-specific expression in cervical carcinomas.

METHODS

We used polymerase chain reaction-based techniques, including sequencing, oligonucleotide hybridization, and microsatellite analysis, to identify HLA class I gene defects in two tumor-derived cell lines and to confirm the presence of these defects in the original tumors.

RESULTS

In one tumor, in exon 2 of the HLA-B15 gene, a four-nucleotide insertion resulted in a stop codon in exon 3. In the other tumor, in two duplicated copies of the HLA-A24 gene, single-point mutations resulted in stop codons in exons 2 and 5.

CONCLUSIONS

To our knowledge, this is the first report of HLA class I gene mutations identified in primary tumors that lead to loss of allelic expression in tumor cells. Such tumor-specific mutations may permit the cell to escape HLA class I-restricted cytotoxic T-cell responses.

HLA class I phenotype and genotype alterations in cervical carcinomas and derivative cell lines

Downregulation of HLA class I expression is a common event in tumor biology. Various underlying mechanisms have been defined in different tumors, but the knowledge of HLA loss mechanisms in cervical carcinoma is limited. To identify causalities for loss of surface expression, we performed a detailed investigation of HLA class I phenotypes and genotypes in 5 primary cervical tumors and on derivative cell lines. Protein expression on primary tissues and cell lines was evaluated by immunohistochemistry and flow cytometry respectively, using a broad panel of allele-specific monoclonal antibodies. Loss of expression was seen in 3 cases, comprising B15-locus loss, B15-allelic loss, and loss of an A74/B15 haplotype and an A24 allele of the other haplotype. Cytokine treatment induced re-expression of the B15-locus loss, suggesting a regulatory defect underlying lack of constitutive expression in this tumor. In contrast, molecular analyses at the DNA and/or RNA level showed that the other, non-inducible, losses were associated with chromosomal HLA gene defects. Loss of heterozygosity analysis was performed to confirm larger genomic deletions. This study shows that HLA gene defects by mutation or loss of heterozygosity as well as regulatory defects are involved in cervical carcinogenesis. The resulting changes in HLA expression may directly affect the efficacy of the immune response to these human papillomavirus-related neoplasms. Heterogeneity in the underlying loss mechanisms may offer individual tumors various opportunities to escape immune surveillance, and may severely compromise T-cell based therapy.

Peptides derived from the whole sequence of BCR-ABL bind to several class I molecules allowing specific induction of human cytotoxic T lymphocytes

Chronic myeloid leukemia (CML) is characterized cytogenetically by a t(9;22) translocation which generates a hybrid bcr-abl gene, encoding a p210(bcr-abl) fusion protein. The induction in vitro of leukemia-specific T cells reactive with p210(bcr-abl) is a strategy developed for an immunological therapeutic approach in CML. Peptides from the junction region of this chimeric protein have been considered as potential targets for a cytotoxic response against leukemic cells. However, only a few peptides encompassing the two p210(bcr-abl) breakpoints have been shown to bind to the most common HLA class I molecules, which limits the number of patients who could benefit from this approach. We assume that the presence of chimeric BCR-ABL protein in leukemic cells may affect processing and delivery of peptides, possibly giving rise to new epitopes at the cell surface. We selected 162 peptides from the whole sequence of this protein, including 14 peptides of the b2a2 and b3a2 junctions, which had an anchor motif for a common HLA class I molecule. We tested their ability to bind to eight HLA class I molecules (HLA-A1, -A2, -A3, -A11, -B7, -B8, -B27, -B44). We identified 48 peptides from outside the junction region, with intermediate or strong binding capacities to these HLA class I molecules contrasting with only six junction peptides with a moderate binding capacity to HLA-A3/A11, -B8, or -B44 molecules. Moreover, cytotoxic T lymphocyte lines specific for various peptides outside the junction were generated from peripheral blood mononuclear cells of HLA-A2 or -B7 healthy donors and from one CML patient. These results contribute to evaluation of immunity to the BCR-ABL chimeric protein. Further studies are required to investigate whether such epitopes are correctly processed and presented by leukemic cells.

HLA-dependent variations in human immunodeficiency virus Nef protein alter peptide/HLA binding

In human immunodeficiency virus (HIV) infection, sequence variations within defined cytotoxic T lymphocyte (CTL) epitopes may lead to escape from CTL recognition. In a previous report, we have shown that the variable central region of HIV Nef protein (amino acids 73-144) that contains potential CTL epitopes, can escape the CTL response. We suggested that this non recognition occurs through a variety of mechanisms. In particular, we provided evidence that HIV Nef sequences recovered from HLA-A11-expressing individuals have alterations in the major anchor residues essential for binding of the two Nef epitopes (amino acids 73-82 and 84-92) to the HLA-A11 molecule. Here, we investigate in more detail whether variations in autologous Nef sequences affect HLA binding, leading to CTL escape. Potential epitopes were sought by testing Nef peptides containing the HLA-A11-specific motif or related motifs. We confirmed that only the two previously described epitopes identified in cytolysis tests have optimal reactivity with the HLA-A11 molecule. We then sequenced several viral variants from donors that do not express the HLA-A11 molecule and compared the variability of these epitopes with those obtained from HLA-A11-expressing individuals. One substitution (Leu85) found in the sequences isolated from both populations increase the reactivity of the HLA-A11-restricted epitope 84-92, and might explain the difference in immunogenicity observed between the two HLA-A11-restricted epitopes from HLA-A11+ individuals. In addition, selective variations were only detected in virus isolated from HLA-A11-expressing individuals. Furthermore, examination of the association of variant peptides with the HLA-A11 molecule demonstrated that a single substitution within the minimal epitope could not always completely abrogate HLA binding, suggesting that multiple alterations within a particular epitope may accumulate during disease progression, allowing the virus to escape CTL recognition.

Impaired cytotoxic T lymphocyte recognition due to genetic variations in the main immunogenic region of the human immunodeficiency virus 1 NEF protein

Human immunodeficiency virus (HIV) induces strong responses from human histocompatibility leukocyte antigen (HLA) class I-restricted cytotoxic T lymphocytes (CTL). In a previous report we identified an immunodominant region (amino acids 73-144) in the NEF protein that was recognized by CD8+ class I-restricted CTL of most asymptomatic individuals. Analysis of the 73-144 region by peptide sensitization, experiments using overlapping peptides corresponding to the LAI isolate identified the peptide sequences located between residues 73 and 82 or 84 and 92 and the peptide sequence between residues 134 and 144 as cognate peptides for HLA-A11- and HLA-B18-restricted epitopes, respectively. This report describes the variable demonstrable reactivities of CTL obtained from HLA-A11 or HLA-B18 seropositive, asymptomatic patients who all had a response to the virus NEF protein, but who did not always recognize appropriate cognate peptides. The high mutation rate of HIV probably facilitates the selection of mutants that can avoid the cellular immune response. We therefore analyzed the variability of these epitopes restricted by HLA-A11 and HLA-B18. We sequenced several viral isolates from HLA-A11 and HLA-B18 donors who recognized certain HLA-peptide complexes and from those who did not. A CTL sensitization assay was used to show that some mutations led to a great reduction in CTL activity in vitro. This might be due to failure of the mutated epitope to bind major histocompatibility complex class I molecule. A simple assay was used to detect peptides that promoted the assembly of class I molecules. Some of these mutations at major anchor positions prevented HLA-A11/peptide binding, and consequently impaired recognition of the HLA-peptide complex by the T cell receptor.

Locus-specific analysis of human leukocyte antigen class I expression in melanoma cell lines

Surface expression of human leukocyte antigen (HLA) class I antigens on melanoma lines was evaluated by locus-specific monoclonal antibodies (mAbs) with three different techniques: Fluorescence-activated cell sorting (FACS), immunohistochemistry with cytospin preparation (ICP), and complement-mediated cytotoxicity (CMC). Eleven HLA class I-expressing cell lines developed from metastases were used. Specific expression of HLA loci was examined under routine culture conditions and after 48-h incubation in interferon-gamma (IFN-gamma; 500 U/ml). Loss of allelic expression was seen in one line (586-MEL): Products of genes coding for HLA-A29 and -B44, in strong linkage disequilibrium, were not detectable. HLA-A antigens were consistently detected by all methodologies and minimally affected by pretreatment with IFN-gamma. HLA-B antigens were detectable in 8 of 11 lines by ICP and 3 of 11 lines by CMC. By FACS the supratypic specificity HLA-Bw6 was expressed at low levels in most lines (mean fluorescence 47.2 +/- 13.4 and rose to 259.8 +/- 45.9 after incubation with IFN-gamma; p < 0.001). HLA-Cw antigen detection by CMC correlated with HLA-B (p < 0.01), suggesting that down-regulation and sensitivity to IFN-gamma are shared by the two loci. This low expression of the HLA-B antigens may play a role in the evasion of the host immune response and its up-regulation may be useful in allowing tumor antigen recognition.

Recognition of HLA-A1 by murine monoclonal antibodies

Balb/c mice were immunized with cells from the mouse mastocytoma line P815 transfected with an HLA-A1 gene. The splenocytes of the immunized mice were fused with cells from the murine myeloma NS-1. In an initial screening, supernatants of growing cultures were tested for their binding capacity to the immunizing P815/A1+ cells as well as to P815/A2+ cells. Three out of 756 hybrids produced antibodies which bound to P815/A1+ cells only. They were cloned and further analyzed for their binding reactivity to reference B-lymphoblastoid cells from the Tenth International Histocompatibility Workshop. One monoclonal antibody, designated 6B11, reacted only with HLA-A1+ cells, while the two other antibodies, 3G3 and 7F10, appeared to detect antigenic determinants shared by HLA-A1, A3, A11, A26, and A30 (3G3) and by HLA-A1, A3, A11, A26, A28 and A30 (7F10). Flow cytometric studies on B-lymphoblastoid cell lines as well as on a series of tumor cell lines, including melanoma and colon carcinoma lines, confirmed the specificity of these antibodies. Monoclonal antibodies 7F10 and 6B11 were found to be of the IgM class and 3G3 of the IgG1 class. By complement-dependent 51Cr release experiments it was further shown that the two IgM antibodies 7F10 and 6B11 were able to lyse all cell lines of the HLA-A1 haplotype tested.

Generation of a human hybridoma producing a pure anti-HLA-A2 monoclonal antibody

We report the production and characterization of a human monoclonal IgM hybridoma antibody recognizing antigen HLA-A2. B lymphocytes obtained from the peripheral blood of a multiparous volunteer 1 week postpartum were transformed in vitro by Epstein-Barr virus, screened by a microlymphocytotoxicity assay, and electrofused with the heterohybridoma fusion partner, K6H6/B5. A specifically anti-A2 secreting hybridoma cell line. MBW1, was then identified and cloned. The cytotoxic IgM antibody produced showed complete correlation (r = 1.00) with the A2 antigen on a large panel of unrelated donors' lymphocytes, and no cross-reactivity with A28, Aw68, or Aw69 antigens was observed.

DNA sequence of HLA-A11: remarkable homology with HLA-A3 allows identification of residues involved in epitopes recognized by antibodies and T cells

The human class I alleles HLA-A11 and HLA-A3 have a well-documented history of serological cross-reactivity. This cross-reactivity suggests that they are closely related, a suggestion which is supported by the fact that the HLA-A11 and HLA-A3 genes are distinguished from all other A-locus genes by a restriction fragment length polymorphism observed in Bam HI digests. To examine the extent of sequence homology between HLA-A11 and HLA-A3, we have cloned the HLA-A11 gene and sequenced the coding regions (exons). The results reveal that HLA-A11 and HLA-A3 display the highest degree of homology reported for any pair of serologically defined class I alleles. Only nine base differences resulting in six amino acid differences were observed in exons 2-8. One of the amino acid substitutions is in the alpha 1 domain and the other five are in the alpha 2 domain. comparison of this sequence with that of other human class I molecules implicates Gln62 as a critical residue involved in HLA-A11 - HLA-A3 serological cross-reactivity. In addition, the amino acid sequence allowed us to successfully predict cross-reactive recognition of HLA-A11 by cytotoxic T lymphocytes specific for a rare subtype of HLA-A3, HLA-A3.2. This result provides further support for the importance of the alpha 2 domain residues 152 and 156 in forming determinants on class I molecules that are recognized by cytotoxic T lymphocytes.